I have migrated from Windows 7 to Ubuntu just yesterday. Windows 7 was in my C: drive. I did not realise that if I wipe Windows 7 and install Ubuntu, Ubuntu would be installed in the C: drive only. So I didn't make any backups, and I deleted Windows and installed Ubuntu. But, Ubuntu has formatted my hard drive and I have lost all my important data!

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I am just a beginner in UBUNTU. will you please tell me step by step process. my hdd is SATA 500 GB, OS- ubuntu 12.10 and i have a live USB of ubuntu 12.10
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nurul islamJan 23 '13 at 6:10

the C drive is completely irrelevant to ubuntu. Drive labelling is actually just an abstraction given by windows. In actual fact the C drive is just a part of your hard drive called a partition. Windows will always label the partition it is installed to C. When you installed ubuntu it didn't just use this partition, it used the entire drive, because that is what you told it to do. I'm afraid I find windows use of the name "drive" rather annoying, as it confuses users into thinking a partition is a "drive".
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handuelApr 4 '13 at 17:00

Optionally (but highly advisable) and if we had an external drive big enough to hold all of the faulty drive we can make a backup to recover data or partitions from an image. Make this image with the following command in a terminal:

sudo dd if=/dev/sdX of=/path/to/external_drive/backup.img

Replace sdX with the drive to recover. Since dd is an advanced and potentially harmful tool take extra care to not accidentally overwrite any drive you may still need.

In case you are unable to recover your partitions you may be able to recover single files by running PhotoRec wich comes with the TestDisk suite.

in my hdd i had around 40 GB of impotent data which i want to recover. Now i have an external usb drive (pen drive) of 8 GB, is it possible to copy the recovered data by PhotoRec in multiple session (pause and resume) on pendrive and transfer it to another pc or i have to run PhotoRec too many time to copy data.
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nurul islamJan 24 '13 at 5:09

@nurulislam: it is possible to recover files by a single type only but you may have more than 8 GB of files of a single type. It is therefore strongly advisable to have an external strorage medium at hand which is big enough to hold all of the recovered files. BTW PhotoRec will not recover paths or filenames.
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TakkatJan 24 '13 at 9:20

(For those who have the opposite problem: you think you've formatted the Ubuntu partition).

try booting using the bootable Ubuntu CD/DVD or USB drive and start partitionmanager/gparted in it.

1) BAD SCENARIO
It either should display that the partition is still using Ubuntu filesystem (typically ext4) or not. If you've formatted the Ubuntu partition (ext4) in Windows to the NTFS filesystem, than the data are very likely gone. :-(((

2) Good scenario
If the partition is there and you simply cannot boot to the Ubuntu, try this guide to restore the (grub) boot chain:

I highly recommend adding that information to your answer. (Also note that testdisk will install fine in a live environment, so a live CD/DVD or live USB works OK for this purpose.)
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Eliah KaganJan 22 '13 at 6:47

I am just a beginner in UBUNTU. will you please tell me step by step process. my hdd is SATA 500 GB, OS- ubuntu 12.10 and i have a live USB of ubuntu 12.10
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nurul islamJan 23 '13 at 6:11